It seems to me that when it starts up, the column nearest the TRV gets hot but before the rest of the rad has warmed up it's turned itself off. I've tried opening up the lock valve on the other end to get more flow through, but it's the same. The pump is running at its fastest setting.
Would it make better sense to have the TRV on the other end? What's the normal convention? The TRV has arrows on it indicating it will operate with the flow in either direction.